1. Field of the Invention
The present invention relates to an electron beam curing resin for a magnetic recording medium, a method for manufacturing the same, and a magnetic recording medium including the same. In particular, it relates to an electron beam curing resin having a high cross-linking property suitable for the magnetic recording medium use, a method for manufacturing the same, in which an electron beam curing resin having a high cross-linking property is produced by modifying a general thermosetting vinyl chloride resin or polyurethane resin to become sensitive to an electron beam, and a magnetic recording medium including the same.
2. Description of the Related Art
Known resins used for magnetic recording media primarily include thermosetting resins and electron beam curing resins. Among them, the thermosetting resin is cured by a method in which active hydrogen groups typified by a hydroxyl group present in the resin and isocyanate compounds are reacted so as to effect cross-linking of the resin. On the other hand, the electron beam curing resin is cured by a method in which electron beam sensitive type functional groups typified by an acrylic double bond are introduced in a molecule of the resin, and cross-linking of the resin is effected by electron beam irradiation.
In general, electron beam curing resins used for magnetic recording media include vinyl chloride resins and polyurethane resins. Examples of methods for modifying the vinyl chloride resins to become sensitive to an electron beam include a method in which hydroxyl groups in a thermosetting vinyl chloride resin having the hydroxyl groups are reacted with tolylene diisocyanate (TDI) adducts resulting from a reaction between tolylene diisocyanate (TDI) and 2-hydroxyethyl methacrylate (2-HEMA), as disclosed in Japanese Examined Patent Application Publication No. 1-25141, a method in which hydroxyl groups in a vinyl chloride resin are reacted with cyclic acid anhydrides and, furthermore, an epoxy monomer having an acrylic double bond is reacted, as disclosed in Japanese Patent No. 2514682, and a method in which hydroxyl groups in a vinyl chloride resin are reacted with 2-isocyanate ethyl (meth)acrylate (MOI), as disclosed in Japanese Unexamined Patent Application Publication No. 4-67314.
On the other hand, with respect to the polyurethane resin, typical examples of methods include a method in which a (meth)acrylate compound having hydroxyl groups in a molecule is used as a part of the raw materials for synthesizing the polyurethane and, thereby, a radiation curing polyurethane resin is produced, as disclosed in Japanese Patent No. 2610468 and a method in which a polyurethane having isocyanate groups at polymer terminals is prepared and, subsequently, is reacted with alcohol having an acrylic double bond, as disclosed in Japanese Examined Patent Application Publication No. 3-1727.
However, with respect to known electron beam sensitive modified materials of vinyl chloride resins or polyurethane resins, coating films do not always have adequate cross-linking properties. Furthermore, if the concentration of hydroxyl groups in the resin is increased in order to improve the cross-linking property, a problem occurs in that the viscosity of the paint is increased.